1. Field of the Invention
Embodiments of the invention relate to high velocity engines and projectiles. More particularly, embodiments of the invention relate to testing procedures and apparatuses for high velocity engines and projectiles.
2. Description of Related Art
Ramjet and supersonic combustion ramjet (scramjet) technology has been the subject of extensive research and development. In this application, the term ramjet is intended to include scramjets, where appropriate. Scramjet engines provide propulsion at hypersonic speeds (i.e., above Mach 5) by capturing atmospheric air to burn onboard fuel. For hypersonic propulsion, these air breathing engines are more efficient than rocket motors and can allow longer duration hypersonic flight with greater payload.
Testing scramjet engines has, in the past, been an extremely expensive undertaking. This is due to the need to accelerate a scramjet to its takeover velocity, the velocity at which the engine begins to be able to operate. The takeover velocity is at supersonic or hypersonic speeds. One mainstream thought regarding methods of accelerating a scramjet engine to the takeover velocity involves a first stage vehicle being lifted to flight level by a jet aircraft and released. The first stage vehicle then accelerates the scramjet vehicle beyond the takeover velocity, at which point the scramjet engine ignites and testing can begin. The costs associated with one such test can be on the order of magnitude of $10 million. The high cost of such testing has proved to be prohibitive in many cases, resulting in insufficient testing of scramjet technology.
As a low cost alternative, it has been proposed to use a gas gun to accelerate to supersonic speeds a projectile having a scramjet engine. Many problems exist with the prior art ramjet test projectile and with methods for launching such a ramjet test projectile from a gas gun. For example, the acceleration forces to which a ramjet, and particularly a scramjet, projectile are subjected during a gas gun launch is more than 5000 G's and is more typically on the order of 10,000 G's, that is, 10,000 times the force of gravity, or more. Launches from other types of guns can subject a scramjet or other projectile to 60,000 or 70,000 G's. At accelerations as high as these, the projectile must be G-hardened to withstand the loads resulting from the acceleration. Conventional mechanical fasteners often used in the prior art cannot withstand such forces. Moreover, the basic structural design of prior art ramjet projectiles is incapable of withstanding such forces. Prior ramjet test projectiles typically include a heavy center body surrounded by a cowl. Thin pylons are used to hold the center body and cowl together. When a projectile having such a construction is subjected to the high acceleration forces present during gun launch, the thin pylons break and the test projectile disintegrates.